LNB Performance Study

Transcription

1 Page 1 of 46 ERA TECHNOLOGY LNB Performance Study Z Wang I Parker B Randhawa A Ishaq ERA Project 7G FINAL REPORT Client : Ofcom Client Reference : Stephen Talbot ERA Report Checked by: Approved by: S P Munday Project Manager Ofcom Measurement Resource M Ganley Programme Manager Ofcom Measurement Resource February 2007 Ref: SPM/vs/62/03452/Rep-6078

2 2 Copyright ERA Technology Limited 2007 All Rights Reserved No part of this document may be copied or otherwise reproduced without the prior written permission of ERA Technology Limited. If received electronically, recipient is permitted to make such copies as are necessary to: view the document on a computer system; comply with a reasonable corporate computer data protection and back-up policy and produce one paper copy for personal use. Distribution List Client (1) Project File (1) DOCUMENT CONTROL If no restrictive markings are shown, the document may be distributed freely in whole, without alteration, subject to Copyright. ERA Technology Ltd Cleeve Road Leatherhead Surrey KT22 7SA UK Tel : +44 (0) Fax: +44 (0) info@era.co.uk Read more about ERA Technology on our Internet page at:

3 3 Summary Ofcom is currently consulting on proposals to award spectrum in the 10 GHz band between GHz paired with GHz. The spectrum between GHz is used globally for satellite service in the space to Earth direct. In the UK the vast majority of installations are for the reception of direct-to-home satellite television. In order to investigate potential blocking of the satellite signal from out-of-band emissions, Ofcom commissioned ERA Technology to examine the potential interference from the proposed 10 GHz band allocations to the direct-to-home satellite service band. Measurements were made at ERA s test facility in Leatherhead, Surrey, on three Low Noise Block (LNB) converters in common use in domestic satellite systems. Tests were carried out to measure the gain of the LNBs, the received satellite signal level, the thirdorder intermodulation products, and performance blocking of satellite systems in domestic usage. The results show that for the three LNBs tested, gain varies slightly across the operational frequency band, and it rolls off quickly outside the operational band. The average gain measured is shown in the table below. Invacom LNB (conducted) Invacom LNB (radiated) Sharp LNB (radiated) MTI LNB (radiated) Average Gain (db) Standard Deviation (db) Received satellite signal levels were measured on all the transponder centre frequencies of ASTRA 2A/2B/2D and Eurobird_1 satellites. The measurements were carried out for three different weather conditions: sunny, raining and cloudy as different types of weather will cause different received signal levels. The radiated measurements were carried out with clear-blue sky and cloud cover conditions and the actual weather status during the project was noted. The average received signal level at the measurement site for all conditions is summarised in the table below. ASTRA Eutelsat (Eurobird_1) Average received satellite signal level 1 (dbm) Standard Deviation (dbm) Third order intermodulation measurements were carried out for all three LNBs. Conducted measurements were used for the Invacom LNB and a radiated measurement method was used for the 1 The signal levels were the level at the input flange of the LNB.

4 4 other two LNBs. The Output third-order Intercept Point (OIP3) and Input third-order Intercept Point (IIP3) are shown in the table below: LNB Invacom LNB Sharp LNB MTI LNB OIP3 (dbm) IIP3 (dbm) Third order intermodulation (TOI) products were measured to assess the required input signal level to cause TOI products: at the same level of the received satellite signal (-90 dbm) at a level 10 db lower than the received satellite signal (-100 dbm). The threshold of input power level of f1 and f2 are shown in the table below: Signal level of TOI product equal to input power level of -90 dbm (dbm) Signal level of TOI product equal to input power level of -100 dbm (dbm) Input power level before LNB (f1 = 11.5 GHz and f2 = GHz) Input power level before LNB (f1 = GHz and f2 = GHz) No TOI products were observed or distinguishable from the noise floor using one tone from the LNB band with an operational signal level of -65 dbm (before LNB) and one tone from the Ofcom proposed 10 GHz band using a signal level to cause the onset of saturation (-50 dbm). Performance blocking measurements were carried out with both in-band and out-of-band Continuous Wave (CW) interferer, and with a wideband Additive White Gaussian Noise interferer. The average measured C/I due to blocking was: Interferer In-band CW signal Out-of-band CW signal Out-of-band AWGN signal Average measured C/I ratio due to blocking (db) Standard Deviation (db) EIRP (dbw) from interferer (22.5m away in the bearing direction)

5 5 Contents Page No. 1. Introduction Background LNBs in Common Use in the UK Market Frequency Bands used by Satellite Transponder/LNB Measurements Methods LNB Gain Conducted measurement Radiated measurement Received Satellite Signal Strength Third Order Intermodulation Products Frequency Blocking Performance Results LNB Gain Received Satellite Signal Strength Third Order Intercept Points Third Order Intermodulation Products TOI products generated by tones from Ofcom proposed low band and Ofcom proposed high band TOI products generated by tones from Ofcom proposed band and LNB low band Non-Linear Effects of LNB Frequency Blocking Performance 30

6 Co-channel interference Out-of-band narrowband (CW) interference Out-of-band wideband (AWGN) interference Conclusions Test Equipment References 38 APPENDIX A: Gain Measurement Results of LNBs 39 APPENDIX B: TOI Measurement Results of LNBs 44

7 7 Tables List Page No. Table 1: Permissible out-of-block emissions...11 Table 2: Average Gain of LNBs...22 Table 3: Installation Parameters for BSkyB Satellite dish...25 Table 4: Average received satellite signal level...26 Table 5: Average Third-Order Intercept Point of LNBs...27 Table 6: TOI products generated by 11.5GHz and GHz tones...28 Table 7: Possibility of two tones which generate the TOI at LNB band...28 Table 8: TOI products generated by tones of Ofcom proposed low band and high band...29 Table 9: In-band CW interference signal strength due to blocking...31 Table 10: Out-of-band CW interference signal strength due to blocking...33 Table 11: Out-of-band AWGN interference signal strength due to blocking...34 Table 12: Equipments used for the project...37 Table 13: Conducted measured Gain of Invacom LNB...39 Table 14: Radiated measured Gain of LNBs...42

8 8 Figures List Page No. Figure 1: Frequency Plan of Eurobird_1 downlink (only operational channels are displayed)...13 Figure 2: Frequency Plan of ASTRA 2A, 2B and 2D downlink...14 Figure 3: Test set-up for conducted LNB gain measurements...15 Figure 4: Test set-up for measuring antenna receiver gain...16 Figure 5: Set-up to measure TOI products using two-tone testing of NI method...18 Figure 6 Radiated set-up to measure TOI products using two-tone test...19 Figure 7: Test set-up to measure blocking performance...20 Figure 8: View of instrumentation trailer, satellite dish and TV receiver...21 Figure 9: View from dish towards interfering source and satellite position...21 Figure 10: Gain of LNBs at the LNB frequency band...24 Figure 11: Average Field Strength of received satellite signal level...26 Figure 12: TOI measurements for Invacom LNB, Sharp LNB and MTI LNB...45 Figure 13: TOI products generated by two tones from Ofcom proposed bands...46

9 9 Abbreviations List AWGN CW DUT EUT FWA IIP3 IMD3 LNB L.O. MTI OIP3 RBW TOI VBW VSWR Additive White Gaussian Noise Continuous Wave Device Under Test Equipment Under Test Fixed Wireless Access Input third-order intercept point Two-tone third-order intermodulation distortion Low Noise Block Local Oscillator Microelectronics Technology Inc Output third-order intercept point Resolution Bandwidth Third Order Intermodulation Video Bandwidth Voltage Standing Wave Ratio

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11 11 1. Introduction Ofcom is currently consulting on proposals to award spectrum in the 10 GHz band between GHz paired with GHz. In the UK, the spectrum between GHz is used for the reception of direct-to-home satellite television. There is a total of 2 x 100 MHz of spectrum available in the 10 GHz band. Ofcom is proposing to offer this as a single UK lot. In arriving at this proposal Ofcom considered two options: offering two separate 100 MHz lots or a single paired 100 MHz lot [1]. The regulator has identified a number of potential applications, which fall broadly into three categories: Mobile and fixed network operators who might use spectrum to backhaul their own networks. The interest here is in paired spectrum. Fixed Wireless Access (FWA) network operators who might deploy broadband access networks in addition to providing backhaul, both for themselves and for other network operators. The interest here is primarily in paired spectrum. Broadcasters who might use spectrum in the 10 GHz band for video links and wireless cameras. The interest here is in unpaired spectrum. Annex 5.i of Reference [1], gives the maximum Effective Isotropic Radiated Power (EIRP) in the proposed blocks as 55 dbw in any measured bandwidth. The permissible out-of-block emissions are described in the table below: Table 1: Permissible out-of-block emissions Offset from Edge of Block Maximum Permitted Level (dbw) In block up to and including 14 MHz 55 From 14 MHz up to and including 0 MHz 11 + ( 19 / 14 *Δf 1 ) dbw/mhz 1 From 0 MHz up to and including + 14 MHz ( 13 / 14 *Δf 2 ) dbw/mhz MHz of block edge -52 db/mhz 1 Δf 1 is the frequency offset between -14 MHz to 0 MHz of the block edge limits 2 Δf 2 is the frequency offset between 0 MHz to +14 MHz of the block edge limits Where, 0 MHz is the edge of the block, - is inside the block edge and + is outside the block edge.

12 12 In an environment where use is made of the spectrum that Ofcom is proposing for award for systems that are close to the proposed maximum EIRP and densely deployed, the performance of the domestic satellite system (predominately the LNB) to reject signals outside its tuning range will be required. As those performance figures are not usually published for LNBs, actual measurements have been made. For the purposes of this project, the performance of the systems that are directed to the ASTRA systems at 28.2 E and Eutelsat at 28.5 E have been considered. It is assumed that the vast majority of satellite systems in use in the UK are directed to either or both of the satellites identified. Three commercially available LNBs used in domestic satellite systems have been tested; the assessment on the impact of interference from the proposed new band to the existing LNB band included the following tasks: Measure the received signal strength level at the input flange of the LNB from both satellites ASTRA (2A, 2B and 2D) and Eutelsat (Eurobird 1). Examine the Third Order Intercept (TOI) point created by combining the signals from the LNB band and signals from outside the band (i.e. within Ofcom proposed bands). Examine the conditions of blocking/breakthrough performance of LNB system. 2. Background 2.1 LNBs in Common Use in the UK Market A Low Noise Block downconvertor sits on the end of an arm and faces the parabolic reflector ("dish") which focuses the signals from the "feed horn" of the LNB. It uses the super-heterodyne principle to take a wide block (or band) of relatively high frequencies, amplify and convert them to similar signals carried at a much lower frequency (called intermediate frequency or IF). These lower frequencies travel through cables with much less attenuation of the signal when compared to those frequencies actually received. This results in a much more manageable signal level left on the satellite receiver end of the cable. It is also much easier and cheaper to design electronic circuits to operate at these lower frequencies, rather than the very high frequencies of satellite transmission. In this study, LNB refers to the LNBs designed to operate at Ku band, i.e GHz. There are several types of LNB available in the market: Standard LNB: has a 10.0 GHz Local Oscillator and works in one band. Enhanced LNB: has a Local Oscillator of GHz, and works in GHz. Universal LNB: has two local oscillators of 9.75 and GHz and it works in two bands of and GHz. (22 khz signal switched). The polarisation switching is controlled by dc voltage supplied by the receiver. Usually 12.5v to 14.5v gives vertical and 15.5 to 18v gives horizontal polarisation.

13 13 The following LNBs have been tested in this study, all of which are Universal LNBs, i.e. having two local oscillator frequencies of 9.75 GHz and 10.6 GHz. Universal LNBs are the most widely used type in the UK market: Invacom LNB: SNF dB low noise Universal LNB. The LNB has a C120 circular waveguide interface, which can attach an external feed horn. Sharp LNB: BS1R6El low noise Universal LNB. Microelectronics Technology Inc (MTI) LNB: AP8-T2RC, 06dB low noise Universal LNB. 2.2 Frequency Bands used by Satellite Transponder/LNB Both ASTRA (2A, 2B and 2D) and Eutelsat (Eurobird 1) satellites use a set of transponders to transmit signals towards the UK and Europe. Figure 1 [2] and Figure 2 [3] indicates the downlink spectrum allocated for domestic satellite broadcast services. Figure 1: Frequency Plan of Eurobird_1 downlink (only operational channels are displayed)

14 14 Figure 2: Frequency Plan of ASTRA 2A, 2B and 2D downlink There are a total of 24 operational transponders on the Eurobird_1 satellite. The transponder bandwidth is 33 MHz (D channels) or 72 MHz (C and F channels) as shown in Figure 1. Across Band E and Band F, there are 40 transponders/channels on ASTRA 2A and 2B, the channels are identical as redundant services while ASTRA 2D is operated at Band D only. The transponder bandwidth of ASTRA is either 33 MHz or 26 MHz. Each transponder broadcasts several TV channel programmes simultaneously. 3. Measurements Methods 3.1 LNB Gain A literature survey was carried out to review available information regarding received signal strength at the LNB. No published information was found to be available and so measurements were first undertaken to characterise the gain of the LNBs Conducted measurement The test set-up for conducted measurements of the LNB gain for the Invacom LNB is shown in the figure below. This was the only LNB that had a C120 flange, allowing it to be connected to an external feed horn, or waveguide. (RF ports on the other LNBs were not accessible.) The Invacom LNB was connected to a cable-waveguide with a WR75 adapter and WR75/C120 transformer. A test signal was transmitted at the required frequency points to the LNB via the adapter, and the output from LNB was linked to a Biased-T, which provided a DC voltage to the LNB via an F-cable and only allowed the RF component to the spectrum analyser. The LNB has an F type connector which is 75Ω, therefore a matched pad was used to connect to the 50Ω input of the signal generator and spectrum analyser, thus ensuring the correct Voltage Standing Wave Ratio (VSWR). The test set-up is shown in the following figure.

15 15 Signal Generator Transition/ Adaptor LNB Biased-T Spectrum Analyser DC Supply Figure 3: Test set-up for conducted LNB gain measurements The gain of the LNB was measured using the following procedure: 1. The input of the LNB was generated by using a Continuous Wave (CW) RF output from a signal generator, in the 11.7 GHz to GHz band. 2. The output from the LNB to the spectrum analyser was used to measure the peak power in a 1 MHz bandwidth with max hold. The gain was calculated as the difference between the measured peak power before and after the LNB. A series of frequency points across the LNB band were measured to see how the gain varied across the band and how the gain fell off out of band Radiated measurement Radiated measurements of LNB gain were made inside a Fully Anechoic Room (FAR), which satisfies the Rayleigh criterion of d > 2D 2 /λ, where D is the maximum dimension of the EUT (in our case the size of the LNB) and λ is the wavelength of interest.

16 16 Figure 4: Test set-up for measuring antenna receiver gain Following the method described in ETSI ETS , the test arrangement was set-up as shown in Figure 4, with the EUT connected to the test receiver, and the following test procedure was used: a) A test signal at the required frequency was transmitted by the test transmitter through the test antenna in the E-plane 2. (The frequency is dependent upon the designed receive frequency band.). b) The EUT was aligned to the transmitting antenna, at a distance of 4m away. c) The EUT was manually tuned in azimuth and elevation directions until the maximum output reading was obtained on the spectrum analyser. d) The EUT was replaced by a substitution antenna. e) This level was read on the spectrum analyser. f) The substitution antenna was tuned in azimuth and elevation directions as in c) until the received signal level was maximised. g) The gain of the EUT was calculated from: G EUT = L1 - L2 + C, where: G EUT is the gain of the EUT (dbi); L1 is the level obtained with the EUT (db); L2 is the level obtained with the substitution antenna (db); C is the calibrated gain of the substituted antenna at the test frequency (dbi). The gain of the LNB G LNB = G EUT - G ANT, assuming the gain of the receiving antenna is known. 2 The E-plane is in the vertical direction

17 17 h) The tests in b) to f) were measured for frequencies in the 10.7 GHz to GHz band. 3.2 Received Satellite Signal Strength The received signal strength measurements were carried out at centre frequencies of all operating multiplexes across the concerned frequency band for both satellites. Currently, there are three ASTRA satellites with either 16 or 40 transponders available for transmission of broadcast and broadband multimedia services for UK and Ireland, and 24 transponders are available from Eutelsat system ( Eurobird ) at 28.5 E, in the bands GHz. The GHz downlink is split into two bands and down converted by a Universal LNB, which has local oscillator(s) working at 9.75 and/or 10.6 GHz. The signal levels of these transponders across the LNB band were examined at centre frequencies of the operating transponders. The received signal strength measurements were performed with a dish that is in common use in direct-to-home systems (typically 60 cm diameter parabolic reflector) using the procedure outlined below: 1. For each satellite, the installation of satellite dish/lnb was aligned to obtain the best reception. The alignment was performed using a hand portable satellite signal strength meter and satellite compass to identify the satellite, and checked with the satellite receiver and television. As different types of weather cause different received signal levels, the radiated measurements were carried out with clear-blue sky, rainy days and cloudy days during the project, which were noted. 2. The measurement result was calculated for the signal received in the 11 GHz band, and not the level from the LNB output (i.e. between MHz), by correlating against the gain of the LNB as measured in Section Steps 1 and 2 were repeated for a number of transponders and an average was taken for the two satellite systems. 3.3 Third Order Intermodulation Products Intermodulation distortion occurs when the non-linearity of a device or system with multiple input frequencies causes undesired outputs at other frequencies. These spurious outputs due to system nonlinearities are the result of mixing of the fundamental and harmonics of other signals (i.e., intermodulation interference). The easiest form of intermodulation interference assessment is to measure two-tone, third-order intermodulation. In the case where two signals are present, the two signals (f 1 and f 2 ) mix with each others second harmonic (2f 1 and 2f 2 ) and create distortion products evenly spaced around the fundamental (2f 1 -f 2 and 2f 2 -f 1 ). These distortion products can degrade the performance of the communication system. Two-tone third-order intermodulation distortion (IMD 3 ) is the measure of the third-order distortion products produced by a non-linear device when two tones closely spaced in frequency are fed into its

18 18 input. This distortion product is usually so close to the carrier that it is almost impossible to filter out and can cause interference in multi-channel communications equipment. Assuming that the power levels of the two tones are equal, IMD 3 is the difference between the power of the fundamental signals and the third-order products, as defined in the following equation: IMD = P o P 3 o3 Where o refers to the output of the EUT, P o3 is the power level of one of the output third-order products, and Po is the power level of one of the fundamental tones. Once the IMD 3 is measured, the EUT output third-order intercept point (OIP3) is calculated using the following equation: IMD3 1 OIP3 = + P = ( P P ) ( db) o 0 o3 The input third-order intercept point (IIP 3 ) is defined as: IIP 3 = OIP o G Where G is the gain of the device. The IIP 3 number quantifies the third-order linearity of a device. The Third Order Intermodulation (TOI) using the two-tone method was measured with the set-up shown below. [4] Figure 5: Set-up to measure TOI products using two-tone testing of NI method

19 19 Figure 6 Radiated set-up to measure TOI products using two-tone test The output third-order intercept point (OIP3) was calculated by following the procedure detailed below: 1. Two tones f 1 and f 2 with a separation of 0.2 MHz were created using signal generator 1 and 2 respectively. 2. The signal level of both tones at the output of the combiner was set to a value of 20 to 30 db above the sensitivity of the LNB. 3. The spectrum analyser was tuned to the third-order distortion product frequency of interest, either 2f 1 -f 2 or 2f 2 -f 1. The resolution bandwidth was then deceased until a distortion spur appeared. 4. The attenuation level was increased until the harmonic level stopped decreasing. The attenuation does not lower the distortion products of the signal; it only lowers the distortion products generated internally to the Equipment Under Test (EUT). The resolution bandwidth was decreased to lower the noise floor. 5. The IMD 3 and IIP 3 points were calculated by measuring the output of the fundamental P o and the third harmonic P o3 and using the equations described above. NOTE: Theoretically, IIP 3 is not a function of power level. However, the dynamic range is limited by the spectrum analyser noise floor at the low end and the DUT saturation or spectrum analyser

20 20 intermodulation at the high end. Looking at IIP 3 as a function of power provides a good way of checking the valid measurement range. 3.4 Frequency Blocking Performance The purpose of this part of the work was to determine the unwanted mixing with the local oscillator, which for most dual band LNBs are: 9.75 and 10.6 GHz. d h Figure 7: Test set-up to measure blocking performance Blocking was measured by setting up the satellite receiving system with the antenna on a tripod (at 1m height), suitably aligned for optimum satellite signal reception, and introducing an interference signal into the main receiving beam. The dish was connected to a Sky digital box with its output fed to a television inside a trailer to enable the picture quality to be assessed. The antenna radiating the interfering signal down towards the receiving dish was at a height of 9.5m and a slant distance of about 22.5m. This was to ensure that the main beam of interfering signal was in the same direction as the satellite signals. A signal generator at ground level was connected to the interfering signal antenna via a 10m microwave coax cable. The set-up is shown in the figures below.

21 21 Figure 8: View of instrumentation trailer, satellite dish and TV receiver Figure 9: View from dish towards interfering source and satellite position The measurement procedure is outlined below: 1. The satellite receiver was mounted on a tripod 1 m above the ground in an open area environment and suitably aligned for optimum satellite signal reception using the procedure described in Section An interfering signal was introduced into the main beam of the receiving satellite antenna. The antenna dish was connected to a standard Sky Digital box decoder with its output fed to a television inside a trailer, where the picture quality was assessed. Before connecting the television the wanted carrier power C of the received satellite signal was measured in the channel bandwidth of the transmitted signal. 3. With no applied signal, the interfering signal antenna was raised into the main beam until a fractional signal reduction was observed and then lowered by 0.4 m to obtain a full line-ofsight signal between the receiving antenna and the transmitting antenna. 4. The interfering antenna was positioned on a pole and raised to its position using an extending mast.

22 22 5. A CW signal was applied in accordance to the emission mask detailed in Table 1 and the level of received interference I measured in the same channel bandwidth as observed for the wanted carrier C. 6. The Carrier-to-Interference C/I ratios due to blocking were calculated as C (dbm) I (dbm). 4. Results 4.1 LNB Gain The conducted and radiated measurement methods described in section 3.1 were used to measure the LNB gain. The average results within the operational frequency band are shown in the table below; the input and output powers measured for each frequency are listed in Appendix A. Table 2: Average Gain of LNBs Average Gain (db) Standard Deviation (db) Invacom LNB (conducted) Invacom LNB (radiated) Sharp LNB (radiated) MTI LNB (radiated) 62.0 db 60.8 db 65.8 db 65.7 db 3.1 db 2.5 db 2.4 db 2.6 db Outside of the operational frequency band the gain of LNBs tested was found to roll off quickly. When the frequency is 500 MHz outside the nominal LNB frequency band, the gain rolls off to about 30 db or lower, as shown in Figure th order polynomial trend lines are shown in Figure 10(b). The gain values outside the LNB band are also listed in Appendix A.

23 LNB Gains Sharp Radiated MTI Radiated Invacom Radiated Invacom conducted Ofcom band Frequency (GHz) Gain (db) (a) Gain of LNBs

24 LNB Gains Sharp Radiated MTI Radiated Invacom Radiated Invacom conducted Ofcom band Poly. (Sharp Radiated) Poly. (Invacom Radiated) Poly. (Invacom conducted) Poly. (MTI Radiated) Frequency (GHz) Gain (db) (b) Trends of Gain Figure 10: Gain of LNBs at the LNB frequency band

25 Received Satellite Signal Strength The field strengths of the satellite signals at the nominal centre frequencies of ASTRA2A/2B/2D /Eurobird_1 transponders were measured using the method described in section 3.2. The centre frequencies of the satellite transponders are shown in Figure 1 and Figure 2. Two ASTRA transponders were found to be non-operational during the measurements, at GHz and GHz. All the Eutelsat transponders shown in Figure 2 were observed with carrier transmissions during the measurements. 3 The measurements were carried out on the roof of a two-storey office building, at the ERA site, located at 51º18 20 N, 0º20 15 W, 44m elevation above sea level. A 60cm BSkyB satellite dish was mounted on a tripod with a height of 1.5m above the roof. The installation parameters shown in the table below were calculated using an online satellite installation tool [5]. Three different weather conditions were observed: Raining (light shower), cloudy and sunny without cloud (just after a shower). Table 3: Installation Parameters for BSkyB Satellite dish ASTRA 28.2º E Eutelsat 28.5º E Dish azimuth (to true north) º º Dish azimuth (to magnet north) º º Dish elevation 25.5 º 25.4 º Polarisation tilt º º The signal from the LNB was transmitted to a BSkyB satellite receiver connected to a television to: Verify the test signals picked up were from the correct satellites. Monitor the TV channels themselves. The average received signal level at the measurement site for all conditions is summarised in the table below. 3 The TV channel information for each satellite transponder could be found at the following links, for ASTRA: and for Euro_bird:

26 26 Average received satellite signal level 4 (dbm) Table 4: Average received satellite signal level ASTRA Eutelsat (Eurobird_1) Standard Deviation (dbm) The average level of received satellite signal is plotted in Figure 11. The plot shows the signal level before LNB and after the 60cm satellite dish as a function of frequency Received ASTRA/Eurobird Satellite Signals ASTRA 2A/2B/2D Eurobird_1 Power level (dbm) Frequency (GHz) Figure 11: Average Field Strength of received satellite signal level 4.3 Third Order Intercept Points Third Order Intercept Points were measured for all three LNBs using the method described in section 3.3. The conducted measurement method was applied for the Invacom LNB (Figure 5) and the radiated measurement method was used for the Sharp LNB and MTI LNB (Figure 6). 4 The signal levels were the level at the input flange of the LNB.

27 27 The frequency span and RBW/VBW of the Spectrum analyser were optimised for observation of intermodulation products as described in intermodulation measurement studies [6, 7]. For this type of measurement, a frequency span of 1 MHz and a RBW/VBW of 1 khz was applied respectively. The frequency of tone 1, denoted as f1, was set to 11.5 GHz and frequency of tone 2, f2, was set to GHz. The input power of f1 and f2 were first set at a low power level between -80 dbm to -75 dbm. At these levels Third Order Intermodulation products were not detectable or distinguishable from the noise floor at the signal generator. The input power was then increased in steps of 3 db, and the output power of the two tones, which was measured at corresponding down-converted frequency after the LNB in lieu of the input frequency f1, was increased proportionally. Input power was increased until the onset of saturation appeared. The measurement results of the Third-Order Intercept points of the three LNBs are shown in Appendix B. The average Output third-order intercept points (OIP3) and the input third-order intercept points (IIP3) are listed in Table 5. The points around noise floor and saturation were not included in the calculation. Table 5: Average Third-Order Intercept Point of LNBs LNB Invacom LNB Sharp LNB MTI LNB Gain at 11.5GHz (db) OIP3 (dbm) IIP3 (dbm) In order to assess the possible interference to the satellite services in the LNB band, two input power levels were examined: The level required to introduce a TOI product equal to the average received satellite signal (-90 dbm) The level required to introduce a TOI product equivalent to 10 db below the average received satellite signals (-100 dbm) Table 6 shows the input power levels required to generate TOI products. The results show that an average input power level of dbm was required to generate TOI products equivalent to the received satellite signal strength (-90 dbm before LNB); and dbm was required to generated TOI products 10 db lower than the received satellite signal strength (-100 dbm before LNB).

28 28 Table 6: TOI products generated by 11.5GHz and GHz tones Invacom LNB Sharp LNB MTI LNB Gain of LNB (db) Average received satellite signal level before LNB (dbm) Signal level of TOI product equal to the case with input power level of -90 dbm (dbm) Signal level of TOI product equals to the case with input power level of -100 dbm (dbm) Average Third Order Intermodulation Products The Third Order Intermodulation products were tested across both the Ofcom proposed bands of concern and the LNB band. Observation of the output showed that there was no significant effect while increasing the frequency gap of the two tones, i.e. with the proper input power level, any two tones from the proposed Ofcom bands and/or LNB band can generate third order intermodulation products, as shown in the table below. Table 7: Possibility of two tones which generate the TOI at LNB band Frequency of Tone 1 Frequency of Tone 2 Frequency of TOI products Ofcom proposed low band Ofcom proposed high band LNB Low band Ofcom proposed band LNB low band LNB band Two further measurements were carried out to examine the TOI products: Using two tones, with one tone from Ofcom s proposed lower band and one from Ofcom s proposed higher band, in order to assess the effects on the TOI products with the variation of LNB gain across these two bands. Using one tone from Ofcom s proposed band and one tone from the LNB s lower band, in order to assess the affects on the TOI products in the case of one tone from Ofcom proposed band and the other tone from received satellite signals.

29 TOI products generated by tones from Ofcom proposed low band and Ofcom proposed high band The LNB gain measurements show that the gain rolls off quite sharply outside the LNB band. The Ofcom proposed bands of 2 x 100 MHz are outside the LNB operational band, where the gain at GHz is db lower than the gain in the nominal frequency band. The gain measured across GHz is at the same margin of the average operational gain. In this scenario the frequency of tone 1, denoted as f1, was set to GHz and frequency of tone 2, f2, was set to GHz, i.e. one tone was at Ofcom proposed low band and another tone at Ofcom proposed high band. The measurement results are shown in Appendix B. Table 8 below shows the input power levels required to generate TOI products. The results show that an average input power level of dbm was required to generate TOI products equivalent to the received satellite signal strength; and dbm was required to generated TOI products 10 db lower than the received satellite signal strength. Table 8: TOI products generated by tones of Ofcom proposed low band and high band Invacom LNB Sharp LNB MTI LNB Gain of LNB (db) Average received satellite signal level before LNB (dbm) Signal level of TOI product equals to the case with input power level of -90 dbm (dbm) Signal level of TOI product equals to the case with input power level of -100 dbm (dbm) Average Comparing to Table 6, as the LNB gain at and GHz is lower than the gain across the operational LNB band, to generate a certain level of TOI products the input power level was 9 db higher TOI products generated by tones from Ofcom proposed band and LNB low band In this scenario the frequency of tone 1, denoted as f1, was set to GHz and frequency of tone 2, f2, was set to GHz, i.e. one tone from the Ofcom proposed band and another tone from the existing LNB lower band.

30 30 As before the input power level of f2 was set as the average received satellite signal level (-90dBm before LNB); the power level of f1 was increased in 3 db / 5 db steps. The input power level of f1 was increased until the onset of saturation (-50 dbm before LNB). The expected TOI product in the corresponding LNB band ( GHz) was not distinguishable from the noise floor of the signal generator. The input power of f2 was then increased until 25 db higher than the average received satellite signal level (-65 db before LNB). With the signal level of -50 dbm at f2, the TOI product at the corresponding LNB band ( GHz) was still not distinguishable from the noise floor of the signal generator. (The other TOI product at GHz was observed.) The measurement results indicate that it is unlikely that TOI products will be generated by a combination of one tone from the existing satellite signal and one tone from the proposed Ofcom band. 4.5 Non-Linear Effects of LNB When performing the TOI measurements non-linear effects were observed on all three LNBs. These effects consisted of: frequency shifting, limitation of output power. The frequency shifting was observed when the total current/power load was close to saturation. The maximum observed frequency shift was 22 khz for the Invacom LNB, 8 khz for the Sharp LNB and 10 khz for the MTI LNB. The non-linear effects of gain can be observed in Figure 12 and Figure 13, when the LNBs were overloaded and saturation occurred. 4.6 Frequency Blocking Performance The purpose of the performance/blocking measurements was to make a practical assessment of the level of interference needed to cause blocking effects to the satellite receiving system. The interference sources considered were Third-Order intermodulation products co-located at the satellite operational carrier band; a narrow band signal (CW) at the proposed Ofcom 10 GHz band; a wideband signal (AWGN) at the proposed Ofcom 10 GHz band.

31 Co-channel interference A co-channel unmodulated CW interference signal was used to represent the TOI products that could interfere with a domestic satellite broadcast service. The frequency of the CW signal was set at the centre frequency of the relevant satellite transponder. Using the test method described in section 3.4, the amplitude of the interfering signal was progressively increased until interference on the TV was observed. Tests were made for a number of TV channels corresponding to the operational frequencies of the satellite services, for co-polar antenna orientations (both vertical and horizontal polarisations). Table 9 shows a summary of the results from the measurements. The EIRP was calculated based on that the interference source was 22.5m away from the satellite dish in the bearing direction. The Gain of dish is 34dB assuming the efficiency of the antenna is 55%, and the free space loss propagation is applied for the calculation. Satellite Transponder Table 9: In-band CW interference signal strength due to blocking Freque ncy (GHz) Pol SKY Channel monitored Received signal level (dbm) Blocking threshold of interference signal (dbm) C/I Ratio (db) ASTRA 2D V 315 Film Eurobird_1 S V 645 Thomas Cook TV ASTRA 2D V 986 BBC 1 West ASTRA 2D H 101 BBC one London Eurobird_1 S H 650 Thane Direct ASTRA 2D H 972 BBC1 Wales ASTRA 2B H 630 QVC ASTRA 2D H 617 Cbeebies Average C/I Standard Deviation EIRP -3.5dB 0.8dB -77dBW ( 22.5m away from the dish in the bearing direction) Out-of-band narrowband (CW) interference A narrow band CW signal was transmitted as the interferer towards the satellite dish, using the test method described in section 3.4. The frequencies of the CW signals were chosen to be at the upper and lower ends of the Ofcom proposed bands ( GHz, GHz, GHz and GHz).

32 32 Measurements were made on TV channels at the lower end of LNB band: ITV1 Anglia West: The TV programme is transmitted on transponder of ASTRA 2D, the central frequency is GHz and it is transmitted in horizontal polarisation. Film 4: The TV programme is transmitted on transponder of ASTRA 2D, the central frequency is GHz and it is transmitted in vertical polarisation. (EPG channel 315) Within the LNB operational band, blocking was observed with co-polar antenna orientations at frequencies of GHz and GHz. Outside of the operational band ( GHz) the LNB gain rolls off sharply, decreasing by 20 db or more compared to the in-band gain. With the available interference signal strength, no performance blocking was observed outside of the operational band. An average C/I ratio of -34 db was required to block the performance of satellite services as shown in the following table. The values are the signal level recorded before the LNB and after the satellite dish.

33 33 Table 10: Out-of-band CW interference signal strength due to blocking Wanted Satellite Signal Interference with Sharp LNB Interference with Invacom LNB Interference with MTI LNB Average C/I Standard Deviation EIRP Signal Polarisation Horizontal Vertical Frequency (GHz) TV channel ITV Anglia West Film 4 Received Satellite Signal Level (dbm) Interference Signal strength at GHz (dbm) C/I (db) Interference Signal strength at GHz C/I (db) Received Satellite Signal Level (dbm) Interference Signal strength at GHz (dbm) C/I (db) Interference Signal strength at GHz C/I (db) Received Satellite Signal Level (dbm) Interference Signal strength at GHz (dbm) C/I (db) Interference Signal strength at GHz C/I (db) db 2.5 db -48 dbw ( 22.5m away from the dish in the bearing direction) Out-of-band wideband (AWGN) interference Out-of-band blocking performance was also measured with a wideband (80 MHz bandwidth) signal (AWGN) acting as the interference source. Using the test method described in section 3.4, the centre frequency of the AWGN signal was set to GHz, towards the upper end of the Ofcom proposed bands. As before, measurements were made on TV channels at the lower end of the LNB band, ITV Anglia West ( GHz) and Film 4 ( GHz)

34 34 Within the LNB operational band, blocking was observed with co-polar antenna orientations. An average C/I ratio of -26 db was required to block the performance of satellite services as shown in the following table. The values are the signal level recorded before the LNB and after the satellite dish. Table 11: Out-of-band AWGN interference signal strength due to blocking Wanted Satellite Signal Interference with Sharp LNB Interference with Invacom LNB Interference with MTI LNB Average C/I Standard Deviation EIRP Signal Polarisation Horizontal Vertical Frequency (GHz) TV channel ITV Anglia West Film 4 Received Satellite Signal Level (dbm) Interference Signal strength at GHz C/I (db) Received Satellite Signal Level (dbm) Interference Signal strength at GHz C/I (db) Received Satellite Signal Level (dbm) Interference Signal strength at GHz C/I (db) db 2.3 db -56 dbw ( 22.5m away from the dish in the bearing direction)

35 35 5. Conclusions Measurements have been undertaken at ERA s test facility in Leatherhead, Surrey, on three Low Noise Block (LNB) downconvertors in common use in domestic satellite systems to determine the interference potential from Ofcom s proposals to award spectrum in the 10 GHz band. Tests were carried out to measure the gain of the LNBs, the received satellite signal level, the thirdorder intermodulation products, and performance blocking of satellite services. The results show that for the three LNBs tested, gain varies slightly across the operational frequency band, and it rolls off quickly outside the operational band. The average gain measured is shown in the table below. Average Gain (db) Standard Deviation (db) Invacom LNB (conducted) Invacom LNB (radiated) Sharp LNB (radiated) MTI LNB (radiated) Received satellite signal levels were measured at all the transponder centre frequencies of ASTRA 2A/2B/2D and Eurobird_1 satellites. The measurements were carried out for three different weather conditions: sunny, raining and cloudy. As different types of weather will cause different received signal levels, the radiated measurements were carried out with clear-blue sky and cloud cover conditions and the actual weather status during the project was noted. The average received signal level at the measurement site for all conditions is summarised in the table below. ASTRA Eutelsat (Eurobird_1) Average received satellite signal level 5 (dbm) Standard Deviation (dbm) Third order intermodulation measurements were carried out for all three LNBs. Conducted measurements were used for the Invacom LNB and a radiated measurement method was used for the other two LNBs. The Output third-order Intercept Point (OIP3) and Input third-order Intercept Point (IIP3) are shown in the table below: 5 The signal levels were the level at the input flange of LNB.

36 36 LNB Invacom LNB Sharp LNB MTI LNB OIP3 (dbm) IIP3 (dbm) Third order intermodulation (TOI) products were measured to assess the required input signal level to cause TOI products: at the same level of the received satellite signal (-90 dbm) at a level 10dB lower than the received satellite signal (-100 dbm). The threshold of input power level of f1 and f2 are shown in the table below: Signal level of TOI product equal to input power level of -90 dbm (dbm) Signal level of TOI product equal to input power level of -100 dbm (dbm) Input power level before LNB (f1 = 11.5 GHz and f2 = GHz) Input power level before LNB (f1 = GHz and f2 = GHz) No TOI products were observed or distinguishable from the noise floor using one tone from the LNB band with an operational signal level of -65 dbm (before LNB) and one tone from the Ofcom proposed 10 GHz band using a signal level to cause the onset of saturation (-50 dbm). Performance blocking measurements were carried out with both in-band and out-of-band Continuous Wave (CW) interferer, and with a wideband Additive White Gaussian Noise interferer. The average measured C/I due to blocking was: Interferer In-band CW signal Out-of-band CW signal Out-of-band AWGN signal Average measured C/I ratio due to blocking (db) Standard Deviation (db) EIRP (dbw) from interferer (22.5m away in the bearing direction)

37 37 6. Test Equipment Table 12: Equipments used for the project Equipment Manufacturer and Model Number ID Number Signal Analyser HP E4407B Microlease Signal Generator HP 83752B Microlease Signal Generator Agilent 83711B Microlease Programmable attenuator Marconi Instruments VSWR Bridge 87A Bias-T B428B 8475 Horn 1 AH system SAS-571 E044 Horn 2 AH system SAS-571 E046 Voltage Supplier /50 ohms transformer Pasternack E029 Satellite dish BSkyB Digital Zone2 60cm, Electronic Link ltd. EL0109 LNB LNB LNB Invacom SNH-031 Sharp MTI Receiver Grundig BSkyB GDS200/2 Adjustable feed horn Cable/WR75 adapter WR75/C120 transformer Digital Satfinder Television Invacom C120 feed Flann 094-SF Swedish Microwave DIGISAT LCD Digix Pre-amplifier HP8449B EMC Hire 4441 Signal Generator Agilent E4438C Signal Generator Agilent E4438C Frequency Mixer Mini-circuits ZMX-10G+

38 38 7. References [1] Ofcom, Office of Communications, Award of Available Spectrum 10 GHz, 28 GHz, 32 GHz and 40 GHz, June [2] Eutelsat, SUMMARY CHARACTERISTICS OF THE EUROBIRDTM 1 SATELLITE, eurobird.pdf [3] SES ASTRA, ASTRA 2A/2B/2D, Direct-to-Home services in the UK and Ireland, [4] NI Application Note, Two-Tone Third-order Intermodulation Distortion Measurement, [5] Satellite dish azimuth and elevation pointing calculator. [6] [7] Maury Microwave, Application note 5C-043, THEORY OF INTERMODULATION DISTORTION MEASUREMENT (IMD) 1999.

39 39 APPENDIX A: Gain Measurement Results of LNBs Frequency Table 13: Conducted measured Gain of Invacom LNB Input level before LNB (dbm) Output after LNB with losses corrections (dbm) Gain (db)

40 40 Frequency Input level before LNB (dbm) Output after LNB with losses corrections (dbm) Gain (db)